U.S. Pat. No. 4,447,073 discloses a passive vehicle suspension system in which a multiple disk friction damper is associated with a hydraulic actuator, which is selectively pressurized by a hydromechanical pressure control system in accordance with the velocity of a road arm and road wheel having an in-arm hydropneumatic spring for supporting the vehicle hull.
The passive road wheel suspension of the '703 patent is useful in association with many off road vehicle operations and, while suitable for its intended purpose, is characterized by providing damping action which is correlated to a static position in which the vehicle hull and road arm have a predetermined relationship. Consequently, there are phases of operation in which the passive road wheel suspension may not provide full damping during extreme jounce and rebound movements of the road arm with respect to the vehicle hull.
Combat vehicles are, at the present time, equipped with such passive suspension systems. These systems consist of either mechanical or hydropneumatic springs in combination with fluid or friction dampers. Numerous concepts for semi-active and active suspension systems whose objects are to improve the ride and the stability of road and rail vehicles have been disclosed in U.S. Pat. Nos. 3,374,005 and 4,194,761. The design of these systems is a compromise between the conflicting requirements for a stiff, heavily damped suspension system to lift the vehicle over terrain disturbances whose amplitude is greater than the available wheel travel and to statically equilibrate and dynamically stabilize the vehicle; and a soft, lightly damped system to isolate the vehicle from terrain disturbances whose amplitude is within the available wheel travel. This compromise, which is generally resolved in favor of permitting the vehicle to traverse rough terrain without bottoming the suspension system, results in a combat vehicle wherein the crew and the equipment's ride quality, the weapon platform's stability, the loss of vehicle contact with the ground, and the amount of energy absorbed combine to limit the mobility, agility, survivability and lethality of the combat system as it travels cross-country. In addition, these compromise suspension systems cause a high force spectral density to be transmitted between the ground and the vehicle so as to reduce the life of track, wheels, and bearings; and the resultant shock and vibration increase the maintenance requirements for the sights, sensors, electronics, etc. Either the size, weight, cost, complexity, energy consumption, reliability, maintainability, durability, or survivability of these systems, when applied to heavy combat vehicles, has precluded their acceptance and adoption. Thus, the interest in and the desire to achieve the potential advantages for combat vehicles with improved suspension systems has been thwarted by the limitations of these suspension systems.